Structural analysis of the catalytically inactive kinase domain of the human EGF receptor 3

Abstract

The kinase domain of human epidermal growth factor receptor (HER) 3/ErbB3, a member of the EGF receptor (EGFR) family, lacks several residues that are critical for catalysis. Because catalytic activity in EGFR family members is switched on by an allosteric interaction between kinase domains in an asymmetric kinase domain dimer, HER3 might be specialized to serve as an activator of other EGFR family members. We have determined the crystal structure of the HER3 kinase domain and show that it appears to be locked into an inactive conformation that resembles that of EGFR and HER4. Although the crystal structure shows that the HER3 kinase domain binds ATP, we confirm that it is catalytically inactive but can serve as an activator of the EGFR kinase domain. The HER3 kinase domain forms a dimer in the crystal, mediated by hydrophobic contacts between the N-terminal lobes of the kinase domains. This N-lobe dimer closely resembles a dimer formed by inactive HER4 kinase domains in crystal structures determined previously, and molecular dynamics simulations suggest that the HER3 and HER4 N-lobe dimers are stable. The kinase domains of HER3 and HER4 form similar chains in their respective crystal lattices, in which N-lobe dimers are linked together by reciprocal exchange of C-terminal tails. The conservation of this tiling pattern in HER3 and HER4, which is the closest evolutionary homolog of HER3, might represent a general mechanism by which this branch of the HER receptors restricts ligand-independent formation of active heterodimers with other members of the EGFR family.EGFR ͉ human epidermal growth factor receptor 3 ͉ human epidermal growth factor receptor4 ͉ receptor oligomerization

ErbB3/HER3 intracellular domain is competent to bind ATP and catalyze autophosphorylation

“…However, structural differences in the N lobe-including the shortened αC-helix-reinforce the argument that ErbB3-TKD cannot be activated (as "receiver") by the same types of interactions thought to activate EGFR, ErbB4, and ErbB2 in heterodimeric complexes. Jura et al (30) very recently reported an ErbB3-TKD 674-1001 structure [Protein Data Bank (PDB) ID 3KEX] that is essentially identical to that reported here and have confirmed the ability of ErbB3-TKD 674-1001 to function as an allosteric activator of EGFR-TKD in vitro. If the ErbB3-TKD does function as a receiver kinase in ErbB receptor dimers, it must do so through N-lobe interactions distinct from those described for EGFR (5) and ErbB4 (27).…”

“…QM/MM simulations also argue that the inactive-like ErbB3-TKD crystal structure presented here and recently by Jura et al (30) can catalyze phosphoryl transfer. Thus, ErbB3 does appear to have an active tyrosine kinase in its intracellular domain.…”

HER3 intracellular domains play a crucial role in HER3/HER2 dimerization and activation of downstream signaling pathways

“…Structural modeling of the intracellular kinase domain region based on a published HER3 kinase model did not reveal major structural differences between wild type HER3, HER3-2-3, and HER3-2-2 (Jura et al, 2009b;Jura et al, 2009a) (Fig. 5).…”

“…HER3 is different from EGFR, HER2 and HER4 in that it lacks intrinsic kinase activity and has not been reported to form homodimers on cell surface (Sierke et al, 1997;Berger et al, 2004). Since the catalytically inactive kinase domain of HER3 is not capable of activating the kinase domain of its partnering receptors, HER3 is suggested to have evolved as a dedicated and specialized activating receptor in the EGFR family (Jura et al, 2009a;Amin et al, 2010a).…”

“…Dimerization among the EGFR family of receptors leads to allosteric activation of the kinase domains of the partners, and the activated kinase domains in turn phosphorylate the tyrosine residues in the C-terminus of the receptors (Jura et al, 2009b;Jura et al, 2009a). HER3 is different from EGFR, HER2 and HER4 in that it lacks intrinsic kinase activity and has not been reported to form homodimers on cell surface (Sierke et al, 1997;Berger et al, 2004).…”